Antonio (a Venetian merchant) is hanging out with his friends Salerio and Solanio on a street in Venice. Antonio is a sad bunny, though he claims he doesn't know why.
Instead of trying to cheer him up, his friends Solanio and Salerio volunteer reasons why he might be depressed. They suggest that maybe he's worried about all the big ventures he's financed at sea. His ships are out there with goods; if they make it back safely, he'll be rich – but if they don't, he'll be in trouble.
Antonio insists that his merchandise at sea is not the cause of his sadness. He's diversified his assets, so no single venture can make or break his fortunes. Even if some ships fail, others are bound to make it. So he's covered – or so he thinks.
Solanio isn't satisfied and suggests that Antonio might be in love. This sounds exciting, and of course we'd like to hear more, but Solanio's gossipy gab is cut off by the entrance of yet more friends: Lorenzo, Graziano, and Bassanio, whom we learn is a great friend of Antonio. Salerio and Solanio hastily take their leave, probably because they know Graziano is going to wax on for longer than they care to stick around.
Indeed here comes the waxing. Graziano has noticed that Antonio looks sad (what, is he wearing a sign?), and again elects not to cheer his friend. Instead, Graziano notes that he'll always be merry, no matter the circumstances. He adds that some men who are quiet and sad-looking seem thoughtful, but they're likely to be as foolish as anyone else; they're just hiding it well.
After making this long-winded point about short-winded people, Graziano exits with Lorenzo, leaving Bassanio and Antonio to talk. Antonio asks about Bassanio's "secret pilgrimage" to see a lady. (Hmm. Could this be the cause of Antonio's sadness?)
Bassanio fills us in: he's been living well above his means for a while now, and it's finally come back to bite him in the nether-regions.
He explains to Antonio that it's to him that he owes the most love and money; therefore he is obligated to reveal a scheme he's concocted to get himself out of debt. He waxes on about how sometimes you have to risk more to gain more. Finally Antonio cuts him off and says he doesn't need to justify himself: Bassanio should know that Antonio will do anything for him. (Just think Brad Pitt and George Clooney in Ocean's Eleven.)
You're probably wondering what Bassanio's story has to do with the lady. Wonder no more. Bassanio has discovered a woman named Portia who has come into a big inheritance in Belmont. She's good looking, but more importantly, she's rich. Lots of men have been trying win her hand, and Bassanio is certain if he could only appear to be as rich or worthy as these other men, he could convince her to marry him. This would solve his debt problems nicely.
Antonio supports this scheme, but unfortunately all of his money is tied up in his sea ventures. Still, he tells Bassanio to try his hand at raising some money around Venice on credit, using his (Antonio's) good name. Antonio adds that he, too, will work on raising some cash. Basically, even if it means stretching his credit to the limit, he's willing to do whatever he can to get Bassanio all set up to woo Portia in Belmont.